Chitin is a valuable substance found in the animal and fungi kingdoms. It is the main component of the cell walls of fungi, the exoskeletons of insects and arthropods (e.g., crabs, lobsters, shrimp, etc.), the radulae of mollusks, and the beaks and internal shells of cephalopods (e.g., squid, octopuses, etc.). Chitin is useful for many medical and industrial purposes. Chitosan is a deacetylated form of chitin which occurs naturally along with chitin in different proportions in various fungal cells. Both chitin and chitosan can serve as raw material for making forms of glucosamine, nutraceuticals for which there is a huge demand.
Glucosamine is considered by many to provide significant therapeutic relief for arthritis and joint pain. Glucosamine may also aid the restoration of cartilage to relieve inflammation in the joints, and is beneficial to both animals and humans. In the Unites States, glucosamine is sold as a dietary supplement for humans, and is prescribed as a supplement for pets. Market size worldwide may be a million tons per year, with a retail value of tens of billions of dollars.
Currently, the main source of commercial glucosamine is crustaceans. The exoskeletons of these organisms are processed to obtain the natural polymer chitin, which is converted into its monomer glucosamine using acid and alkaline production techniques. Chitosan is made by alkaline deacetylation of chitin. These sources provide useful glucosamine for most applications. However, there are a number of limitations on the production and use of these crustacean-based products.
First, the extraction processes employed to convert glucosamine from crustacean chitin produces waste streams have significant environmental impacts. In addition, because many species of crustaceans are involved, the often wild-harvested crustaceans exhibit substantial variations in exoskeleton composition, as the feeds they scavenge on vary extensively. Further, because various toxicants are released in the shallow waters in which the crustaceans live, products derived from these crustaceans may contain significant concentrations of industrial contaminants, including heavy metals. Glucosamine derived from crustaceans is known to contain human allergens that can be dangerous to allergic individuals, which comprise approximately 2% of all adults. The seasonality of harvesting also complicates the steady production of glucosamine.
Moreover, the act of harvesting of crustaceans has significant environmental impacts. The crustaceans are part of the food chain and the harvesting process has detrimental effects on other sea life such as plants and corals.
Some religions also object to ingesting glucosamine derived from crustaceans. Both strict Muslims and Jews reject crustaceans as not being “halal” or “kosher”. Likewise, many Hindus and vegans require glucosamine that is free of products derived from animals, and glucosamine compositions derived from shellfish do not meet these needs. Thus, production of glucosamine from sources other than crustaceans, e.g. derived from fungal biomass, is desirable.
Conventional methods of producing chitin from fungal biomass require a deproteinization step to isolate the chitin. Traditional deproteinization procedures utilize a strong alkali, most typically 10% sodium hydroxide solutions, to produce a mixture of amino acids, saponified fatty acids (lipids) and alkali in water. The problem is that there is no simple way to extract the protein, fatty acids and other components, and particularly to recover the alkali from the biomass. Additionally, to improve the purity of the resultant chitin, washing with water is required, thereby exacerbating the complexity of alkaline extraction and recovery from larger volumes of water, or otherwise creating a waste disposal problem.
Furthermore, after the alkaline extraction utilizing convention methods, the remaining solids are extracted with an alcohol (typically methanol) to remove any residual lipids. The solids are then washed, dewatered, and dried. The extraction process produces a voluminous chitin-rich hydrogel from the fungal biomass. After drying the hydrogel, the volume decreases dramatically and leaves solid chitin. However, depending on the alkaline chemical and processing conditions, the physical nature of the dried chitin can vary greatly. For example, the dried chitin can be in the form of a “chip” or sheet that is either wavy or flat and can be picked up as a single piece. In other cases, a chip or sheet is not produced at all, but instead the chitin remains attached as a coating to the drying equipment and must be scraped out, thereby requiring additional labor, or a different drying method such as spray drying, adding to the cost of the chitin production.
As described in the conventional methods above, isolating chitin from fungal biomass by extracting proteins and oil with a sodium hydroxide solution is effective, but creates messy extracts that make recovery of protein, oil, alkali, and other components difficult.
Therefore, there is a need for an economical method that produces safe, non-animal, high-quality chitin and chitosan for use as the raw material for the production of glucosamine that does not offend religious convictions or exclude users with certain allergies. Furthermore, there is a need for a method that produces chitin or chitosan of consistent quality with minimal environmental impact.